copper powder

Abstract

This copper powder has an average reflectance ΔY of 0.3% or more.

Description

[Technical Field]

[0001] This specification discloses technology relating to copper powder. [Background technology]

[0002] In recent years, a method has been attracting attention in which a conductive film is formed by mixing copper powder with ink or paste to form a conductive coating material, and then applying the conductive coating material and heating it to sinter the copper powder. This method allows for the rapid formation of a conductive film in a desired pattern at a relatively low cost.

[0003] To form a fine pattern of conductive film using this method, fine copper powder is used as the copper powder to be contained in the conductive coating material. However, due to the high surface activity of fine copper powder, the copper particles that make up the copper powder tend to aggregate in the conductive coating material, which reduces the yield of the conductive coating material.

[0004] In this regard, Patent Document 1 proposes a method for producing copper powder, which aims to "provide a method for producing copper powder that can produce copper powder with little particle size variation and excellent monodispersity," and "is characterized by preparing a copper complex ion solution from a copper-containing solution and a complexing agent, and then adding a reducing agent to the copper complex ion solution to precipitate metallic copper." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-241709 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, copper powder that is less likely to aggregate and is easily dispersible in conductive coating materials is required from the viewpoint of improving yield, etc. However, it is difficult to say that the copper powder produced by the method described in Patent Document 1 has sufficiently high dispersibility.

[0007] This specification provides copper powder with excellent dispersibility. [Means for solving the problem]

[0008] The copper powder disclosed in this specification has an average reflectance ΔY of 0.3% or more. and 20% or less and the copper content excluding copper oxide is 98 mass% or more. The BET specific surface area is 1.0m 2 / g~15.0m 2 / g That is it. [Effects of the Invention]

[0009] The copper powder has excellent dispersibility. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a photograph of a membrane filter after suction filtration when the average reflectance ΔY of copper powders of Example 2 and Comparative Example 1 was measured. DETAILED DESCRIPTION OF THE INVENTION

[0011] The embodiments of the copper powder described above will be described in detail below. The copper powder in one embodiment has an average reflectance ΔY of 0.3% or more. Although the reason for this is not entirely clear, it is based on the newly discovered finding that when the average reflectance ΔY is as high as 0.3% or more, the dispersibility of copper powder in the conductive coating material is improved.

[0012] (composition) Copper powder contains copper (Cu) and in many cases is composed mostly of copper. The copper content of copper powder can be confirmed by X-ray diffraction (XRD).

[0013] The copper content of the copper powder excluding copper oxide may be, for example, 98% by mass or more, typically 99.5% by mass or more The copper content is measured by X-ray diffraction (XRD).

[0014] Copper powder may contain citric acid (C6H8O7). For example, copper powder containing citric acid, due to the addition of citric acid during manufacturing, tends to have a spherical shape, which reduces the contact area between copper particles and makes it easier to suppress aggregation.

[0015] The presence of citric acid in the copper powder can be confirmed by identification using a liquid chromatography-Orbitrap mass spectrometer (Thermo Fisher Scientific, LC-Orbitrap MS, LC: Vanquish analytical purification LC system, Orbitrap MS: Orbitrap Exploris 240 mass spectrometer). The measurement conditions are as follows: Copper powder is placed in a solution (1:1 volume ratio) of 10 mmol / L ammonium acetate aqueous solution and acetonitrile (4 mL of mixed solution per 1 g of copper powder). Extraction is performed using a shaker and ultrasonic cleaner. The copper powder and extract are separated by centrifugation, and the extract is collected by syringe filtration (Merck Millipore, Millex®-LCR, material: hydrophilic PTFE, pore size: 0.45 μm). This extract is then measured using the liquid chromatography-Orbitrap mass spectrometer described above. The column is a Hypersil GOLD (C18) column, and the mobile phase is changed from 10 mmol / L ammonium acetate aqueous solution to acetonitrile. The column temperature is 40°C. In negative ion detection mode, if a value close to (±0.5) the m / z value of 191.0192 (the monoisotopic mass of [C6H8O7-H]-, where a proton has been removed from the chemical formula corresponding to citric acid) is detected, it can be said that the copper powder contains citric acid.

[0016] (Average reflectance) The copper powder has an average reflectance ΔY of 0.3% or more. If the average reflectance ΔY of the copper powder is 0.3% or more, the copper powder is less likely to aggregate in the conductive coating material and is sufficiently dispersed. From the viewpoint of improving dispersibility, a larger average reflectance ΔY is desirable, preferably 0.7% or more, more preferably 1.8% or more. The average reflectance ΔY of the copper powder may be 20% or less.

[0017] The average reflectance ΔY of the copper powder is measured as follows. First, a sample is prepared. More specifically, copper powder is mixed with water to form a slurry, and the water content of the slurry is adjusted to 94% to 97% by mass. The container containing the copper powder slurry is then shaken to homogenize the slurry. More specifically, 50 g to 80 g of the slurry is placed in a cylindrical 100 mL plastic container with a lid. The lid is then closed, and the container is shaken up and down at least 25 times every 10 seconds for 3 to 5 minutes. Next, the copper powder slurry is subjected to suction filtration using a Merck MF-Millipore membrane filter with a diameter of 47 mm and a pore size of 0.025 μm, so that the copper powder on the filter is 0.3 g ± 0.05 g. During suction filtration, the slurry is dripped onto the filter to form a pool of liquid, and a suction pump (ULVAC DTU-20) is used to suction the liquid without touching it until it is no longer visible. Suction is continued until the liquid is no longer visible. This allows the copper powder to deposit evenly on the filter.The filter after suction filtration is then dried in the air for at least three hours.This leaves a layer of deposited copper powder on the filter.This filter is then attached to a flat glass plate, taking care not to lift it up, and this is used as the sample.

[0018] Thereafter, the reflectance Y value of the sample is measured. The measurement device used can be an SQ7700 (Nippon Denshoku Industries Co., Ltd.). Here, the measurement is performed with the sample placed upside down so that the hole in the measurement section of the measurement device is completely blocked. The sample is placed upside down in this manner because the measurement device is designed so that light is irradiated from below to above. This allows the reflectance Y value to be measured. Detailed conditions are shown below. Calibration: Use the white standard plate attached to the SQ7700 (Nippon Denshoku Industries Co., Ltd.) Illumination and light receiving conditions: JIS Z8722 compliant di: 8° and de: 8° Light source: D65 Viewing angle: 10° Measuring diameter: φ18mm Color system: Measure reflectance Y value

[0019] Each Y value (spectral reflectance) of the XYZ color system for the SCI method, which includes specular reflected light, and the SCE method, which excludes specular reflected light, is measured using the method described above, and the average reflectance ΔY is calculated from ΔY = (Y value of the SCI method) - (Y value of the SCE method).

[0020] (BET specific surface area) The BET specific surface area of ​​copper powder is 1.0m 2 / g~15.0m 2 / g. It is preferable that the BET specific surface area is 1.0 m 2 If the BET specific surface area is less than 15.0 m / g, there is a concern that the copper powder will not sinter when heated at a relatively low temperature, and that fine wiring using a conductive film will not be realized. 2 If the content exceeds 1 / g, it becomes difficult to ensure the oxidation resistance of the copper powder, and there is a concern that moisture absorption or the like may affect the properties of the conductive coating material.

[0021] From this perspective, the BET specific surface area of ​​copper powder is 2.0m 2 / g~10.0m 2 / g, and 3.0m 2 / g~7.0m 2 / g is even more preferred.

[0022] The BET specific surface area of ​​copper powder can be measured in accordance with JIS Z8830:2013 using, for example, a BELSORP-mini II from Microtrac-Bell Co., Ltd. More specifically, a 3-g sample of copper powder is degassed for 5 hours at 70°C in a vacuum of 10 Pa or less absolute pressure, and then the nitrogen adsorption isotherm is measured by the static volumetric method. The results obtained are analyzed by the BET method to calculate the BET specific surface area.

[0023] (Roughness of the sediment layer) When a copper powder-containing slurry is dried to form a copper powder deposit layer, the arithmetic mean roughness Ra of the surface of the deposit layer is preferably 2.0 μm or less. If the arithmetic mean roughness Ra is 2.0 μm or less, the copper powder has sufficiently high dispersibility, and it is believed that a conductive coating material obtained using such copper powder tends to have effectively dispersed copper powder.

[0024] From the viewpoint of further improving dispersibility, the arithmetic mean roughness Ra of the copper powder deposition layer is preferably 1.5 μm or less, and more preferably 1.2 μm or less. Although there is no particular disadvantage in the case where the arithmetic mean roughness Ra is too small, it may be 0.1 μm or more in manufacturing.

[0025] For the same reason as for the arithmetic mean roughness Ra, the maximum height Rz of the deposited layer of copper powder is preferably 10 μm or less, more preferably 8 μm or less, and may be 1.0 μm or more.

[0026] To measure the arithmetic mean roughness Ra and maximum height Rz, a sample is prepared by preparing a slurry, suction filtering, and drying in the same manner as when measuring the average reflectance ΔY described above. The filter on which a copper powder deposit layer is formed is attached to a glass plate to prepare a sample. The surface texture of this sample is measured in accordance with JIS B0601:2001, and the arithmetic mean roughness Ra and maximum height Rz are determined. The measurement device used is OPTELICS HYBRID (Lasertec Corporation, "OPTELICS" is a registered trademark). Measurements are taken at three locations under the following measurement conditions, and the average values ​​are used as the measurement results. Analysis software: LMeye7 Lens name: TU Plan Apo 50x / 0.80A (Nikon Corporation) Magnification: 50x Resolution: 0.07μm Optical path: confocal Scan Rate: Standard Operating mode: Standard Magnification: 100% Gain: 200 Exposure time: Standard Room temperature: 20~25℃ λs:0.0025mm λc:0.8000mm λf:2.500mm Lc: 0.8 mm Tilt correction: Automatic Capture area: 296.532 μm × 296.532 μm (1024 pixels × 1024 pixels) Analysis range: 200 μm × 200 μm (690 pixels × 690 pixels)

[0027] (Manufacturing method) Copper powder can be produced by various methods, including liquid phase methods such as chemical reduction and disproportionation. For example, in the case of the liquid phase method, it is important to add a predetermined amount of citric acid and adjust the amount of citric acid added at a predetermined time. A specific example of a production method using the chemical reduction method will be described in detail below.

[0028] In the chemical reduction method, copper particles are generated by mixing and reacting a copper salt such as copper sulfate, a reducing agent, and an alkali in a liquid, thereby obtaining a copper slurry containing the copper particles. Examples of reducing agents include hydrazine, hydrazine monohydrate, 1,1-dimethylhydrazine, 1,2-dimethylhydrazine, sodium sulfite, sodium borohydride, sodium bisulfite, hypophosphorous acid, sodium hypophosphite, ascorbic acid, oxalic acid, formic acid, and formaldehyde. Examples of alkalis include sodium hydroxide, ammonia, and potassium hydroxide. If necessary, a pH adjuster such as dilute sulfuric acid or citric acid may also be used.

[0029] In a more detailed example, after heating an aqueous copper sulfate solution to an appropriate reaction temperature, the pH is adjusted with an aqueous sodium hydroxide solution or an aqueous ammonia solution, and then an aqueous hydrazine solution is added all at once to cause a reaction that reduces the copper sulfate to cuprous oxide particles with a particle size of about 100 nm. Then, after heating a cuprous oxide slurry containing the cuprous oxide particles to the reaction temperature, an aqueous solution containing sodium hydroxide and hydrazine is added dropwise, and then an aqueous hydrazine solution is added dropwise to reduce the cuprous oxide particles to copper particles.

[0030] In the above method, when generating cuprous oxide particles, it is preferable to add 20 g to 30 g of citric acid per 50 g of copper powder to be finally produced. Furthermore, after copper particle nuclei are generated, citric acid is also added when terminating the nuclei generation, preferably in an amount of 2 g to 5 g per 50 g of copper powder to be finally produced. If the amount of citric acid added at either stage is too small, the copper powder tends to be dull and have a low average reflectance ΔY. On the other hand, if the amount of citric acid added at at least one stage is too large, reduction to copper may not be achieved. In this case, the copper powder finally produced may contain cuprous oxide or copper hydroxide, resulting in copper powder that is dull and has a low average reflectance ΔY. In addition, if the amount of citric acid added is increased to reduce the copper to copper, the cost of wastewater treatment increases. Furthermore, if the amount of sodium hydroxide is increased, the sodium content of the copper powder increases, and when fine wiring is formed using such copper powder, short circuits are more likely to occur.

[0031] After obtaining the copper slurry containing copper particles as described above, the copper slurry is washed by a filter press, decantation, or the like to perform solid-liquid separation, and then dried and crushed to produce copper powder. [Example]

[0032] Next, the above-mentioned copper powder was produced as a prototype, and its effects were confirmed, which will be described below. However, the description here is for illustrative purposes only and is not intended to be limiting.

[0033] Example 1 200 g of copper sulfate pentahydrate and 25 g of citric acid were dissolved in 725 g of water, and the liquid temperature was raised to above 50°C. A mixture of 800 g of 10 wt% aqueous sodium hydroxide, 100 g of water, and 12 g of hydrazine monohydrate was added. This is believed to have produced cuprous oxide particles. Next, a mixture of 20 g of 10 wt% aqueous sodium hydroxide and 6 g of hydrazine monohydrate was added. 10.8 g of 10 wt% aqueous sodium hydroxide was then added. This is believed to have produced copper particle nuclei. 2.5 g of citric acid dissolved in 20 g of water was then added. This is believed to have stopped the formation of copper particle nuclei. An aqueous solution of 6 g of hydrazine monohydrate and 100 g of water was then added, and the mixture was stirred for 2 hours to attempt the growth of copper particle nuclei. After the reaction was completed, the mixture was repeatedly decanted and washed with water to obtain copper powder.

[0034] Example 2 200 g of copper sulfate pentahydrate and 25 g of citric acid were dissolved in 725 g of water, and the liquid temperature was raised to above 50°C. To this was added a mixture of 800 g of 10 wt% aqueous sodium hydroxide, 100 g of water, and 12 g of hydrazine monohydrate. Next, a mixture of 20 g of 10 wt% aqueous sodium hydroxide and 6 g of hydrazine monohydrate was added. Next, 10.6 g of 10 wt% aqueous sodium hydroxide was added. Then, a solution of 2.5 g of citric acid dissolved in 20 g of water was added. Then, an aqueous solution of 6 g of hydrazine monohydrate and 100 g of water was added, and the mixture was stirred for 2 hours. After the reaction was completed, the mixture was repeatedly decanted and washed with water to obtain copper powder.

[0035] Example 3 200g of copper sulfate pentahydrate and 25g of citric acid were dissolved in 725g of water, and the liquid temperature was raised to above 50°C. To this was added a mixture of 820g of 10wt% aqueous sodium hydroxide, 100g of water, and 18g of hydrazine monohydrate. Then, a solution of 2.5g of citric acid dissolved in 20g of water was added. After this, an aqueous solution of 6g of hydrazine monohydrate and 100g of water was added, and the mixture was stirred for 1 hour. After the reaction was completed, the mixture was decanted repeatedly and washed with water to obtain copper powder.

[0036] Example 4 Copper powder was produced using the production method of Example 1 as a base, but by changing the reducing agent, pH adjuster, and stirring time used until the cuprous oxide was reduced to copper powder.

[0037] (Comparative Example 1) 200 g of copper sulfate pentahydrate and 2.5 g of citric acid were dissolved in 725 g of water, and the liquid temperature was brought to 50°C. To this was added 450 g of a 10 wt% aqueous sodium hydroxide solution. Then, a mixed solution of 100 g of water and 12 g of hydrazine monohydrate was added. After the addition, the liquid temperature was raised to above 50°C, and a mixed solution of 210 g of a 10 wt% aqueous sodium hydroxide solution and 1.2 g of hydrazine monohydrate was added. Then, 40.0 g of a 10 wt% aqueous sodium hydroxide solution was added. Then, a solution of 2.5 g of citric acid dissolved in 20 g of water was added. Then, an aqueous solution of 6 g of hydrazine monohydrate and 100 g of water was added, and the mixture was stirred for 3 hours. After the reaction was completed, the mixture was repeatedly decanted and washed with water to obtain copper powder.

[0038] (Comparative Example 2) 200 g of copper sulfate pentahydrate and 2.5 g of citric acid were dissolved in 725 g of water, and the liquid temperature was brought to 50°C. To this, a mixture of 450 g of 10 wt% aqueous sodium hydroxide, 100 g of water, and 12 g of hydrazine monohydrate was added, followed by stirring for 10 minutes. After stirring, the liquid temperature was raised to 70°C. Then, a mixture of 210 g of 10 wt% aqueous sodium hydroxide and 6 g of hydrazine monohydrate was added, followed by stirring for 5 minutes. Next, 35.0 g of 10 wt% aqueous sodium hydroxide was added, followed by stirring for 5 minutes. After stirring, a solution of 2.5 g of citric acid in 20 g of water was added, followed by stirring for 5 minutes. After this, an aqueous solution of 6 g of hydrazine monohydrate and 100 g of water was added over 2 minutes and 30 seconds, followed by stirring for 1 hour.

[0039] (evaluation) For each of the copper powders obtained in Examples 1 to 4 and Comparative Examples 1 and 2, the BET specific surface area, average reflectance ΔY, and arithmetic mean roughness Ra of the deposited layer were measured according to the methods described above. The results are shown in Table 1. In Table 1, the BET diameter was calculated using the BET specific surface area SSA and true density ρ according to the following formula: BET diameter = 6 / (ρ × SSA). ρ was 8.96 g / cm 3 The roughness Rz is the value obtained for the maximum height using the same method as the above-mentioned method for measuring the arithmetic mean roughness Ra of the deposition layer.

[0040] The copper powders obtained in Comparative Examples 1 and 2 had a smaller average reflectance ΔY than the copper powders obtained in Examples 1 to 4, presumably because the amount of citric acid added when producing the cuprous oxide particles was small.

[0041] For reference, photographs of the membrane filters after suction filtration when the average reflectance ΔY of the copper powders of Example 2 and Comparative Example 1 was measured are shown in Figure 1. It can be seen from Figure 1 that the copper powder of Example 2 has a metallic luster, whereas the copper powder of Comparative Example 1 does not. Although photographs are not shown, the copper powders of Examples 1, 3, and 4 had a metallic luster like the copper powder of Example 2, whereas the copper powder of Comparative Example 2 did not have a metallic luster like the copper powder of Comparative Example 1.

[0042] Furthermore, conductive coating materials were prepared using the copper powders of Examples 1 to 4 and Comparative Examples 1 and 2, and their viscosities were confirmed.

[0043] In Examples 1 and 2 and Comparative Example 1, α-terpineol (80.5 g), oleic acid (6.5 g), and ethyl cellulose (49% ethoxy) 10 (13.0 g) were mixed in a planetary centrifugal mixer to form a vehicle. This vehicle (2.0 g) and copper powder (8.0 g) were mixed in a planetary centrifugal mixer to obtain a conductive coating material.

[0044] In Example 3 and Comparative Example 2, α-terpineol (80.5 g), oleic acid (6.5 g), and ethyl cellulose (49% ethoxy) 10 (13.0 g) were mixed in a planetary centrifugal mixer to form a vehicle. This vehicle (2.0 g), copper powder (8.0 g), and α-terpineol (0.6 g) were placed in a 100 ml container and mixed at 2000 rpm in a planetary centrifugal mixer (THNKY, ARE-310) for 5 minutes to obtain a conductive coating material.

[0045] The viscosity of the conductive coating material prepared as described above was measured using a rotational viscometer MCR102 manufactured by Anton Paar. More specifically, the conductive coating material was placed on a thermostatic plate set at 25°C, and a cone plate (model number: CP25-2) with a cone angle of 2° was used as the measurement jig. The gap setting at the measurement position was 0.1 mm, and the cone plate was pressed against the conductive coating material. Any conductive coating material that protruded from the cone plate was then removed. The measurement program was run over a period of 392 seconds, varying the shear rate from 0 to 1000 s -1 The viscosity of the paste was measured at each shear rate. -1 and 10s -1 The viscosity at this time is shown in Table 1.

[0046] [Table 1]

[0047] From Table 1, it can be seen that the copper powders of Examples 1 to 4 all have a higher average reflectance ΔY and a similarly lower roughness Ra (and Rz) of the copper powder deposit layer compared to the copper powders of Comparative Examples 1 and 2. This suggests that the higher the average reflectance ΔY, the smaller the roughness tends to be.

[0048] Furthermore, the copper powders of Examples 1 to 3, which have a high average reflectance ΔY, have a lower viscosity of the conductive coating material compared to the copper powders of Comparative Examples 1 and 2. Therefore, it is believed that the larger the average reflectance ΔY, in other words, the smaller the roughness of the copper powder deposition layer, the lower the viscosity of the conductive coating material. Here, a low viscosity of the conductive coating material indicates high dispersibility of the copper powder in the conductive coating material. Therefore, it can be said that the copper powders of Examples 1 to 4 have higher dispersibility than the copper powders of Comparative Examples 1 and 2.

[0049] Furthermore, because the copper powder of Example 4 had a small BET diameter, it oxidized and generated heat during the preparation of the conductive coating material, causing it to aggregate. This prevented the preparation of a conductive dispersion, and therefore the viscosity could not be measured. However, this was due to a handling issue, and it is believed that a conductive coating material can be prepared by taking measures such as working in an inert atmosphere (e.g., a nitrogen atmosphere). Furthermore, the copper powder of Example 4 had sufficiently low roughness Ra and Rz compared to the copper powders of Comparative Examples 1 and 2, achieving a roughness of 2.0 μm or less, which is one indicator of roughness. Therefore, it is highly likely that the viscosity of the conductive coating material using the copper powder of Example 4 will also be sufficiently low. Specifically, the viscosity of the conductive coating material prepared using the copper powder of Example 4 is expected to be between that of Comparative Example 2 and Example 1, and closer to that of Example 1 than that of Comparative Example 2.

[0050] From the above, it was suggested that the copper powder described above may have excellent dispersibility.

Claims

1. The average reflectance ΔY is 0.3% or more and 20% or less, The copper content excluding copper oxide is 98% by mass or more, A copper powder having a BET specific surface area of ​​1.0 m 2 / g to 15.0 m 2 / g.

2. 2. The copper powder according to claim 1, wherein the arithmetic mean roughness Ra of the deposited layer of the copper powder obtained by drying a slurry containing the copper powder is 0.1 μm or more and 2.0 μm or less.

3. The copper powder according to claim 1 or 2, which contains citric acid.

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